defmodule Credo.Check.Refactor.MapJoin do
use Credo.Check,
id: "EX4014",
base_priority: :high,
explanations: [
check: """
`Enum.map_join/3` is more efficient than `Enum.map/2 |> Enum.join/2`.
This should be refactored:
["a", "b", "c"]
|> Enum.map(&String.upcase/1)
|> Enum.join(", ")
to look like this:
Enum.map_join(["a", "b", "c"], ", ", &String.upcase/1)
The reason for this is performance, because the two separate calls
to `Enum.map/2` and `Enum.join/2` require two iterations whereas
`Enum.map_join/3` performs the same work in one pass.
"""
]
@doc false
def run(source_file, params \\ []) do
issue_meta = IssueMeta.for(source_file, params)
Credo.Code.prewalk(source_file, &traverse(&1, &2, issue_meta))
end
defp traverse(
{{:., _, [{:__aliases__, meta, [:Enum]}, :join]}, _,
[{{:., _, [{:__aliases__, _, [:Enum]}, :map]}, _, _}, _]} = ast,
issues,
issue_meta
) do
new_issue = issue_for(issue_meta, meta[:line], "Enum.join")
{ast, issues ++ List.wrap(new_issue)}
end
defp traverse(
{:|>, meta,
[
{{:., _, [{:__aliases__, _, [:Enum]}, :map]}, _, _},
{{:., _, [{:__aliases__, _, [:Enum]}, :join]}, _, _}
]} = ast,
issues,
issue_meta
) do
new_issue = issue_for(issue_meta, meta[:line], "|>")
{ast, issues ++ List.wrap(new_issue)}
end
defp traverse(
{{:., meta, [{:__aliases__, _, [:Enum]}, :join]}, _,
[
{:|>, _, [_, {{:., _, [{:__aliases__, _, [:Enum]}, :map]}, _, _}]},
_
]} = ast,
issues,
issue_meta
) do
new_issue = issue_for(issue_meta, meta[:line], "|>")
{ast, issues ++ List.wrap(new_issue)}
end
defp traverse(
{:|>, meta,
[
{:|>, _,
[
_,
{{:., _, [{:__aliases__, _, [:Enum]}, :map]}, _, _}
]},
{{:., _, [{:__aliases__, _, [:Enum]}, :join]}, _, _}
]} = ast,
issues,
issue_meta
) do
new_issue = issue_for(issue_meta, meta[:line], "|>")
{ast, issues ++ List.wrap(new_issue)}
end
defp traverse(ast, issues, _issue_meta) do
{ast, issues}
end
defp issue_for(issue_meta, line_no, trigger) do
format_issue(
issue_meta,
message: "`Enum.map_join/3` is more efficient than `Enum.map/2 |> Enum.join/2`.",
trigger: trigger,
line_no: line_no
)
end
end